Image sensor and method of manufacturing the same

ABSTRACT

On a transparent electrically insulating substrate, formed are a scanning line, and a gate electrode of a switching element, further formed are a gate insulating film, a semiconductor layer, an n + -Si layer to be formed into a source electrode and a drain electrode. After the patterning of the foregoing structure, the dielectric film is formed, and the portion corresponding to the contact hole is removed by etching, and photosensitive resin is applied to form the interlayer insulating film. Then, the transparent electrode is extended from the pixel electrode over the switching element, whereon a conversion layer and a gold layer for use in electrode are vapor-deposited. In this structure, an increase in capacitor between the pixel electrode and the signal line can be suppressed by the interlayer insulating film, and the transparent electrode functions as a top gate and release excessive electric charge. As a result, excessive electric charge can be released effectively in the double gate structure while suppressing an increase in capacitor between the pixel electrode and the signal line.

FIELD OF THE INVENTION

[0001] The present invention generally relates to an image sensor forconverting an incident electromagnetic wave such as a light beam or anX-ray into electric charge and outputting an image signal bysequentially reading out the electric charge, and also relates to amethod of manufacturing such image sensor.

BACKGROUND OF THE INVENTION

[0002] A known active matrix substrate for use in a liquid crystaldisplay device, etc., includes a plurality of independently driven pixelelectrodes arranged in a matrix form, and switching elements such asTFTs (Thin Film Transistors), etc., provided for respective pixelelectrodes. In the liquid crystal display device adopting such activematrix substrate, an image is displayed by sequentially selecting theswitching elements by scanning lines and reading potentials of signallines into the pixel electrodes via the switching elements.

[0003] The foregoing active matrix substrate can be used for an imagesensor. Examples of known image sensors adopting the active matrixsubstrate include: an image sensor including a conversion layer formedon an upper layer of the active matrix substrate, for directlyconverting incident electromagnetic wave such as a light beam, an X-ray,etc., into electric charge, wherein the electric charge generated fromthe conversion layer is stored in pixel capacitance at high voltage, andthe electric charge is read out sequentially from the pixel capacitance.For example, Japanese Unexamined Patent Publication No. 212458/1992(Tokukaihei 4-212458) published on Aug. 4, 1992, discloses an imagesensor of the above type wherein electric charge as generated by theconversion layer is stored in auxiliary capacitance, and data (potentialdata) are stored in respective pixels in the form of electric chargeaccording to the characteristics of an object. As in the case of theaforementioned liquid crystal display device, by sequentially scanningthe scanning lines, for example, the data stored in a pixel selected bya scanning line is read out and transmitted via a switching element to asignal line, and an image projected to the image sensor is read out froma circuit such as an operation amplifier provided on the other end ofthe signal line.

[0004] The active matrix substrate, which is a precursor to the sensorin the foregoing example can be manufactured at low costs withoutrequiring any additional facilities, because the manufacturing processfor liquid crystal display devices can be used for the manufacturingprocess of image sensors only by adjusting the dimensions of the pixelcapacitance and the time constants of the switching elements to beoptimal for image sensors.

[0005]FIG. 6 is a cross-sectional view illustrating a schematicstructure of a known example of the basic image sensor adopting anactive matrix substrate. The structure illustrated in FIG. 6 isdisclosed in AM-LCD'99 “Real-time Imaging Flat Panel X-Ray Detector” byM. Ikeda, et al. As illustrated in FIG. 6, the active matrix substrateof this sensor is prepared by forming a switching element 51 on atransparent insulating substrate 55, and further vapor-depositingthereon a conversion layer 66 and a metal layer 67 in this order. Theswitching element 51 is prepared by forming on the transparentinsulating substrate 55, a gate electrode 56, an auxiliary capacitanceelectrode (not shown), a gate insulating film 57, a semiconductor layer58, an n⁺-Si layer 59 to be patterned into a drain electrode, a metallayer 60 and a transparent electrically conductive film 61 to bepatterned into a source signal line, and a protective film 62 in thisorder, thereby forming a substrate of the image sensor. The conversionlayer 66 is provided for converting an X-ray into electric charge. Themetal layer 67 is patterned into an electrode for use in applying avoltage to the conversion layer 66. In the foregoing structure, thetransparent electrically conductive film 61 is patterned into the pixelelectrodes for storing the electric charge as converted in theconversion layer 66.

[0006] In the image sensor, the electric charge is read out fromrespective pixel electrodes in contrast to the liquid crystal displaydevice in which electric charge is applied to the pixel electrodes.Therefore, if a normal readout operation of a predetermined cycle is notperformed due to any failure, or a trouble in signal readout program,unexpectedly large electric charge may be stored in the pixel electrode,and the resulting high voltage may cause a damage on the active matrixsubstrate. The foregoing problem is discussed in “Characteristics ofdual-gate thin film transistors for applications in digital radiology”(NRC'96) in “Can. I. Phys. (Suppl)74 published in 1996, in which thefollowing structure has been proposed as a solution to the problem. Thatis, a pixel electrode is extended over a switching element, so that thepixel electrode can be functioned as one of the gate electrodes of adual-gate transistor, and at or above a predetermined threshold voltage,the transistor is switched on, and excessive electric charge isreleased.

[0007] The structure of an image sensor which is particularly effectivein preventing the foregoing problem will be explained in reference toFIG. 7. As illustrated in FIG. 7, the image sensor has a so-called“mushroom structure” wherein pixel electrodes 72 and source lines 71 areformed in different layers so as to be insulated by an insulating layer73 formed in-between, so that the entire channel region W of atransistor 74 is covered with the corresponding pixel electrode 72. InFIG. 7, the reference numerals 75, 76, 77, 78 and 79 indicate a gateelectrode, a drain electrode, an auxiliary capacitance, a conversionlayer and a semiconductor layer respectively.

[0008] The foregoing structure of Waechter, et al, illustrated in FIG. 7is effective for the high voltage protection in the pixel electrodes 72.As to the size of the pixel electrodes 72, however, significantimprovement from the aforementioned active matrix substrate illustratedin FIG. 6 cannot be expected. It is generally known that the larger isthe area occupied by the pixel electrodes 72, the more efficiently, theelectric charge generated from the conversion layer 78 can be collectedin the pixel electrodes 72. In the generally used active matrixsubstrate, however, there is a limit for an increase in size of eachpixel electrode as pixel electrodes are arranged in a plane with certainintervals from source bus lines.

[0009] In the foregoing structure of FIG. 7 wherein the insulating film73 is formed between the source line 71 and the pixel electrodes 72, thepixel electrodes 72 can be formed over the source lines 71 whilemaintaining the insulation between them. In this state, theelectrostatic capacitance is generated between the pixel electrodes 72and the source lines 71, and an overall capacitance of the source lines71 when seen from the side of the signal readout circuit increases, anda noise of the readout signal is increased, resulting in lower signal tonoise (S/N) ratio. For the foregoing reasons, the structure of FIG. 7would not offer any significant improvement in size of the pixelelectrodes 72 from the conventional active matrix substrate.

[0010] In the X-ray image sensor, generally a large pixel capacitance isensured. For this reason, the capacitance between the pixel electrode 72and the source line 71 becomes a load capacitance to the source line 71directly. On the other hand, internal noise generated in the signalreadout amplifier is amplified by a gain in proportion to the ratio ofthe capacitance of the source line 71 to the feedback capacitance. It istherefore effective to reduce the capacitance of the source line 71 fora reduction in internal noise.

[0011] Further, an increase in capacitance of the source line 71 maycause variations in potential of the source line 71 corresponding to thecapacitance CsD (per pixel) between the pixel electrode 72 and thesource line 71 with changes in pixel potential corresponding to the partof the image irradiated with an X-ray. For example, when reading outsignals via the source line 71 with a selection of certain scanningline, the electric charge is kept being stored in other pixelelectrodes, while the electric charge in positive polarity and inproportion to the capacitance CsD are being stored in the source line71. The amount of the electric charge to be stored in the pixelelectrodes and the source line 71 differ depending on the image on anentire screen, thereby presenting a problem that a so-called crosstalkis generated when reading out signals as being affected by pixelelectrodes aligned in direction parallel to the source line 71.

[0012] In order to reduce the capacitance of the source line 71, forexample, an image sensor adopting an interlayer insulating film made ofphotosensitive resin has been proposed, for example, in “Similaritiesbetween TFT Arrays for Direct-Conversion X-Ray Sensors and High-ApertureAMLCDs” (SID 98 DIGEST) by W.den Boer, et al, published in 1998.

[0013] However, W.den Boer, et al does not refer to the dual-gatestructure.

SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide an imagesensor of a dual-gate structure which permits excessive electric chargeto be released effectively while suppressing an increase in capacitancebetween a pixel electrode and a signal line.

[0015] In order to achieve the above object, an image sensor of thepresent invention is characterized by including:

[0016] a conversion section for converting an incident electromagneticwave into electric charge;

[0017] pixel electrodes for storing the electric charge generated by theconversion section;

[0018] switching elements for controlling reading out of the electriccharge from the pixel electrodes;

[0019] an interlayer insulating film made of an organic film formedunder each pixel electrode;

[0020] an electrically conductive film which is electrically connectedto the pixel electrodes, and which is extended from the pixel electrodeto a layer above each switching element; and

[0021] a dielectric layer formed between the switching element and theelectrically conductive film.

[0022] According to the foregoing structure, an interlayer insulatingfilm is formed between the scanning lines, signal lines, and pixelelectrodes in the active matrix substrate. It is therefore possible toform the pixel electrodes over the signal lines. As a result, animproved aperture ratio can be achieved, and in the meantime, byshielding the conversion layer from the electric field generated by thesignal lines and the scanning lines, an operation inferior of theconversion layer becomes less likely to occur.

[0023] Moreover, the organic film of low dielectric constant can beformed thick with ease, and therefore the electrostatic capacitancebetween the pixel electrode and the source signal line can be suppressedto be small. As a result, an increase in noise due to an increase incapacitance of the source signal lines can be prevented, and an improvedsignal to noise (S/N) ratio can be achieved. Furthermore, the activematrix substrate of the image sensor can be manufactured by themanufacturing process of conventional liquid crystal display devicewithout significant modification, and therefore any additional facilityis not needed.

[0024] Furthermore, the electrically conductive film is extended fromthe pixel electrode over the switching element. Therefore, even if anormal readout operation of a predetermined cycle is not performed dueto any failure, or trouble in signal readout program, and unexpectedlylarge electric charge is stored in the pixel electrode, the switchingelement is switched ON at or above a predetermined threshold voltage torelease the excessive electric charge, thereby preventing the switchingelement from being damaged.

[0025] Moreover, by forming the dielectric layer between the switchingelement and the electrically conductive film, such characteristic thatthe thin film transistor is switched ON at or above a predeterminedthreshold voltage is determined by the thickness and the dielectricconstant of the dielectric layer formed between the electricallyconductive film and the switching element, and therefore, the foregoingcharacteristic can be set independently of the interlayer insulatingfilm. Namely, while maintaining optimal excessive voltage dischargecharacteristic, the electrostatic capacitance between the pixelelectrode and the source signal line can be suppressed, and in themeantime, the signal to noise (S/N) ratio can be improved.

[0026] In the foregoing structure, it may be arranged such that in anarea above each switching element, the electrically conductive filmcontacts the dielectric layer without having the interlayer insulatingfilm in between.

[0027] In the foregoing structure, it may be arranged such that theswitching element is a dual-gate transistor, and the electricallyconductive film functions as one of gate electrodes of the dual-gatetransistor.

[0028] In the foregoing structure, it may be arranged such that eachswitching element including its channel region is covered with thedielectric layer,

[0029] the electrically conductive film is extended from the pixelelectrode to an area above the switching element including its channelregion, and

[0030] in an area above each switching element, the electricallyconductive film contacts the dielectric layer without having theinterlayer insulating film in between.

[0031] In the foregoing structure, it may be arranged such that theelectric charge stored in the pixel electrode is a positive charge, andthe switching element conducts with an application of a positive biasvoltage.

[0032] Alternatively, it may be arranged such that the electric chargestored in the pixel electrodes is negative charge, and the switchingelement conducts with an application of a negative bias voltage.

[0033] In the foregoing structure, it may be arranged such that in anarea above the switching element, the interlayer insulating film isformed between the dielectric layer and the electrically conductivefilm.

[0034] According to the foregoing structure, in the area above theswitching element, which has the roughest surface in the active matrixsubstrates formed are not only the dielectric layer but also theinterlayer insulating film made of an organic film. With this structure,even such protrusions and recessions of the rough surface, which cannotbe absorbed completely by the dielectric layer alone, can be absorbed toa sufficient level. In this structure, even when adopting a conversionlayer made of selenium, it is still possible to suppress crystallizationdue to the protrusions and recessions, and therefore films can be formedunder stable conditions.

[0035] In the foregoing structure, the interlayer insulating film may bestructured such that at least a portion above the switching element isformed thinner than other portion of the interlayer insulating film.

[0036] In the foregoing structure, the excessive voltage dischargecharacteristic is determined by the thickness and the dielectricconstant of the interlayer insulating film in the portion between theelectrically conductive film extended from the pixel electrode and theswitching element. It is therefore possible to set the foregoingcharacteristic independently of the interlayer insulating film in theportion for use in forming the electrostatic capacitance between thepixel electrode and the source electrode. Namely, with the foregoingstructure, an improved S/N ratio can be achieved while maintainingoptimal excessive voltage discharge characteristic.

[0037] In the foregoing structure, the interlayer insulating film may bestructured such that at least a portion corresponding to the channelregion of the switching element is formed thinner than other portion ofthe interlayer insulating film.

[0038] In the foregoing structure, a photosensitive organic film may beadopted as the interlayer insulating film.

[0039] According to the foregoing structure, in the area above theswitching element, which has the roughest surface in the active matrixsubstrate, formed are not only the dielectric layer but also theinterlayer insulating film made of the organic film. With thisstructure, even such protrusions and recessions of the rough surface,which cannot be absorbed completely by the dielectric layer alone, canbe absorbed to a sufficient level. In this structure, even when adoptinga conversion layer made of selenium, it is still possible to suppresscrystallization due to the protrusions and recessions, and thereforefilms can be formed under stable conditions.

[0040] In order to achieve the foregoing object, another image sensorfor converting incident electromagnetic wave into electric charge byeach of a plurality of pixel electrodes and outputting image signals bysequentially reading out the electric charge from the pixel electrodesvia switching elements, is characterized by including:

[0041] an electrically conductive film formed so as to be extended fromthe pixel electrode to a portion above each switching element; and

[0042] an interlayer insulating film made of an organic film, formedbelow each pixel electrode and the electrically conductive film, theinterlayer insulating film being structured such that a portion abovethe switching element is thinner than other portion of the interlayerinsulating film.

[0043] In the foregoing structure, the excessive voltage dischargecharacteristic is determined by the thickness of the dielectric constantof the portion between the electrically conductive film extended fromthe pixel electrode and the switching element, and therefore, it ispossible to set the foregoing characteristic independently of theinterlayer insulating film in the portion for use in forming theelectrostatic capacitance between the pixel electrode and the sourceelectrode. Namely, with the foregoing structure, an improved S/N ratiocan be achieved while maintaining optimal excessive voltage dischargecharacteristic.

[0044] In the foregoing structure, it may be arranged such that theinterlayer insulating film is structured such that at least a portioncorresponding to the channel region of the switching element is formedthinner than other portion of the interlayer insulating film.

[0045] In the foregoing structure, it may be arranged such that thechannel region of the switching element contacts the interlayerinsulating film.

[0046] In the foregoing structure, an inorganic film may be adopted forthe dielectric layer.

[0047] In the foregoing structure, it may be arranged such that:

[0048] a double layer structure of the dielectric film of an inorganicfilm and the interlayer insulating film of an organic film is formedunder the pixel electrode,

[0049] in an area above each switching element, the electricallyconductive film contacts the dielectric layer without having theinterlayer insulating film in between.

[0050] In the foregoing structure, it may be arranged so as to furtherinclude:

[0051] a signal line for transferring charge as collected in each pixelelectrode via a switching element,

[0052] wherein the pixel electrode is formed over the signal line havingthe interlayer insulating film in between.

[0053] In order to achieve the above object, a method of manufacturingan image sensor of the present invention is characterized by includingthe steps of:

[0054] forming a plurality of switching elements, a plurality ofscanning lines and a plurality of signal lines on an insulatingsubstrate;

[0055] forming an interlayer insulating film made of a photosensitiveorganic film in respective portions above the plurality of switchingelements, scanning lines and signal lines,

[0056] exposing and developing a resulting photosensitive organic film;

[0057] forming pixel electrodes on the interlayer insulating film; and

[0058] forming conversion means on the pixel electrodes for convertingan incident electromagnetic wave into electric charge,

[0059] wherein exposure with respect to the photosensitive organic filmis varied between at least a portion of an area above each switchingelement and other portion of the photosensitive organic film.

[0060] According to the foregoing structure, the protrusions andrecessions resulting from the patterning of the wires in layer below theinterlayer insulating film can be suppressed by the interlayerinsulating film, and an inferior in characteristics of the conversionmeans for converting an incident X-ray into electric change in upperlayer can be prevented. Moreover, by adopting photosensitive resin, asmooth cross section can be achieved even at the pattern edge of theinterlayer insulating film, and therefore it is possible to more surelyprevent an inferior characteristic of the conversion means. Furthermore,as the pixel electrodes can be formed over the source electrodes, anarea occupied by the pixel electrodes can be increased, and therefore,it is possible to collect the electric charge generated from theconversion means in an efficient manner. In the foregoing structure,even if a normal readout operation of a predetermined cycle is notperformed due to any failure, or trouble in signal readout program, andunexpectedly large electric charge is stored in the pixel electrode, theswitching element is switched ON at or above a predetermined thresholdvoltage to release the excessive electric charge, thereby preventing theswitching element from being damaged. Moreover, while maintainingoptimal excessive voltage discharge characteristics, the electrostaticcapacitance between the pixel electrode and the source signal line canbe suppressed, and in the meantime, the signal to noise (S/N) ratio canbe improved.

[0061] For a fuller understanding of the nature and advantages of theinvention, reference should be made to the ensuing detailed descriptiontaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062]FIG. 1 is a front view illustrating an image sensor in accordancewith one embodiment of the present invention.

[0063]FIG. 2 illustrates a cross section of the portion along an arrowline B-B of the image sensor of FIG. 1.

[0064]FIG. 3 is a cross sectional view of an image sensor in accordancewith another embodiment of the present invention.

[0065]FIG. 4 is a cross sectional view of an image sensor in accordancewith still another embodiment of the present invention.

[0066]FIG. 5 is a cross sectional view of a modified example of theimage sensor of FIG. 4 from which a dielectric layer is omitted.

[0067]FIG. 6 is a cross sectional view of a conventional image sensoradopting an active matrix substrate.

[0068]FIG. 7 is a cross sectional view illustrating the schematicstructure of another conventional image sensor.

[0069]FIG. 8 is a cross sectional view illustrating the schematicstructure of an image sensor.

[0070]FIG. 9 is a cross sectional view illustrating the schematicstructure of another image sensor.

DESCRIPTION OF THE EMBODIMENTS

[0071] To begin with, an image sensor in which pixel electrodes can beformed over source signal lines will be explained.

[0072] The structure of the foregoing image sensor is illustrated inFIG. 8. In FIG. 8, members having the same functions as thoseillustrated in FIG. 6 will be given the same reference symbols.

[0073] In this image sensor, when forming a protective film 62 on atransparent conductive film 61, the portion corresponding to a contacthole 65 of the protective film 62 is removed by etching, and thenphotosensitive resin is applied by the spin coating method to form aninterlayer insulating film 63. Thereafter, a contact hole 65 is formedby the normal photographic process, and a pixel electrode 64 formed onthe interlayer insulating film 63 is connected to the drain electrode ofthe switching element 51 via the contact hole 65.

[0074] In the active matrix substrate manufactured in the foregoingmethod, wherein the interlayer insulating film 63 is formed between thescanning lines and signal lines, it is therefore possible to form thepixel electrode 64 over the signal line. With the foregoing structure,an improved aperture ratio can be achieved. Further, by shielding theconversion layer 66 from the electric field generated by the signallines and the scanning lines, an operation inferior of the conversionlayer 66 can be suppressed.

[0075] Although the pixel electrode 64 is formed over the source signalline, by adopting the interlayer insulating film 63 of a sufficientthickness with low dielectric constant, an increase in capacitance and areduction in S/N can be prevented. Moreover, a slighter greater amountof signals collected that of the image sensor adopting the active matrixsubstrate illustrated in FIG. 6.

[0076] Furthermore, by adopting the dual-gate structure in the foregoingstructure of FIG. 8, an image sensor illustrated in FIG. 9 can beachieved. In FIG. 9, members having the same functions as thoseillustrated in FIG. 8 will be given the same reference symbols. In theimage sensor of FIG. 9, a transparent electrically conductive film 64 aextended from the pixel electrode 64 is formed via the interlayerinsulating film 63. Here, the structure in which the protective film 62is removed in an area above the switching element 51 will be considered.

[0077] As described, when a normal operation is not performed in anevent of a trouble or an error in signal readout program, electriccharge in positive polarity is kept being applied onto the pixelelectrode 64 as illustrated in FIG. 9. In the previous structure of FIG.8, a voltage may be increased to the level at which the switchingelement 51 is destroyed. In contrast, according to the structureillustrated in FIG. 9 adopting the double gate structure, when a pixelpotential is raised to a predetermined threshold voltage, the extendedtransparent electrically conductive film 64 a functions as one of thedual-gate electrodes, and the switching element 51 conducts at lowconductivity, and excessive electric charge is released to the sourcesignal line.

[0078] In the conventional excessive electric charge protectionstructure such as the mushroom structure illustrated in FIG. 7, siliconnitride or silicon oxide is deposited between the top gate 72 and thesemiconductor layer 79 as in the typical active matrix substrate. Assilicon nitride or silicon oxide has a high dielectric constant, due torestrictions in processing or film formation time, it is not possible todeposit such film made of silicon nitride or silicon oxide as thick as afilm made of resin formed by the spin coating method. Therefore, in theresulting structure, it is likely that electric charges is released atrelatively low potential. It is therefore not possible to store a largeamount of electric charge resulting in lower S/N. In view of a storageamount of electric charge, the aforementioned structure of FIG. 9 isadvantageous over the foregoing structure of FIG. 7. As is clear fromthe foregoing explanations, the interlayer insulating film 63 desirablyhas low dielectric constant and is thick. However, when adopting suchinterlayer insulating film 63, a problem arises in that the conductivityof the switching element 51 by the top gate of the dual-gate becomes toolow. Namely, the structure of FIG. 9 adopting the dual-gate structuremay be effective for increasing the capacitance between the pixelelectrode 64 and the source signal line depending on the property of theinterlayer insulating film adopted, however, the function of releasingthe excessive electric charge which is the advantageous characteristicof the dual-gate structure cannot be fully appreciated.

[0079] Depending on the amount of electric charge generated from theconversion layer 66 and the pixel capacitance, only a small amount ofelectric charge may be stored in the pixel electrodes 64. However, inthis case, even if the electric charge starts being released by the topgate before the voltage is raised above a threshold high voltage, thiswould not be a problem. In the case of dealing with very small amount ofelectric charge like the case of the image sensor, variations amongpixels of the switching elements 51 cause a serial problem, andtherefore it is rather preferable to adopt such structure that theelectric charge is released at potential slightly higher than thethreshold potential.

[0080] Namely, when an unexpectedly high voltage of around several tensV is applied to the switching element 51 which is unlikely to generatein the normal operation, even once, a trap potential may be formed inthe gate insulating film 57 or abnormality in characteristic occurs dueto the electric charge being captured. The foregoing abnormality incharacteristic possibly occurs even at relatively low voltage. Forexample, when for some reason, a scanning is stopped in the middle ofthe operation while maintaining signal charge in the pixels, suchabnormality in characteristic possibly occurs even at low voltage withan application of a DC voltage over a long time. Especially, for theimage sensor which deals with signals of very low level, deviations inthe characteristic from the normal value would directly cause deviationsin amount of charge of the signal to be collected. Therefore, thestructure for preventing abnormality in characteristic is needed.

[0081] However, in the foregoing structure of FIG. 9, the switchingelement 51 conducts only at voltage of sufficiently high level, and theelectric charge cannot be released at voltage slightly higher than thethreshold voltage.

[0082] In view of the foregoing, an image sensor of a dual-gatestructure which permits excessive electric charge to be releasedeffectively while suppressing an increase in capacitance between a pixelelectrode and a signal line will be explained in the following firstembodiment of the present invention.

[0083] [First Embodiment]

[0084] The following descriptions will discuss one embodiment of thepresent invention in reference to FIG. 1 and FIG. 2.

[0085]FIG. 1 is a front view of an image sensor in accordance with oneembodiment of the present invention. FIG. 2 is a cross section of theportion along an arrow line B-B in FIG. 1. The image sensor of thepresent embodiment includes a transparent insulating substrate 5, havingformed thereon a scanning line 3, and a gate electrode 6 and anauxiliary capacitance line of a switching element 1. Further laminatedthereon are a gate insulating film 7, a semiconductor layer 8, and ann⁺-Si layer 9 to be patterned into a source electrode and a drainelectrode. Then, the foregoing laminated structure is subjected topatterning. On the n⁺-Si layer 9, further laminated are a transparentdielectric layer 11 and a metal layer 10 for use in a source signal line4, and the resulting laminated structure is subjected to the patterning.

[0086] The wires and the patterns have a double layer structure as inthe foregoing, for purpose of purpose of suppressing problem associatedwith a disconnection of a wire due to dust particles accumulated on alayer and preventing the base layer from being damaged during thepatterning of the overlying metal layer.

[0087] Then, a dielectric layer 22 is formed, and the portioncorresponding to the contract hole 15 is removed by etching. Thereafter,photosensitive acrylic transparent resin is applied by the spin coatingmethod, thereby forming an inter-layer insulating film 13. For thisresin, for example, positive type photosensitive resin may be adopted.The resin has a dielectric constant of 3, and a thickness of 2 μm. Then,as in the normal photographic process, the developing is performed byexposing the area above the switching element 1 and the portioncorresponding to the contact hole 15. As described, after forming aninterlayer insulating film 13, a transparent dielectric layer to bepatterned into pixel electrodes 14 is formed, and is subjected to thepatterning by etching. Here, the pixel electrode 14 is connected to thedrain electrode of the switching element 1 via the contact hole 15through the dielectric layer 22 and the interlayer insulating film 13.

[0088] The essential feature of the image sensor of the presentembodiment lies in that in an area above the switching element 1, thetransparent dielectric layer 14 b extended from the pixel electrode 14is formed via the dielectric layer 22. The dielectric layer 22 isadopted also in the conventional active matrix substrate as a protectivefilm for the purpose of improving the reliability of the switchingelement 1. For this dielectric layer 22, silicon nitride or siliconoxide is typically used. The dielectric film 22 is formed in thicknessof several thousands Å. In the area above the switching element 1, theinterlayer insulating film 13 is removed by exposure and development,wherein the transparent dielectric layer 14 b extended from the pixelelectrode 14 contacts the protective film 22.

[0089] In the image sensor of the present embodiment, a double layerstructure of the dielectric film 22 of an inorganic film and theinterlayer insulating film 13 of an organic film is formed under thepixel electrode 14, and the interlayer insulating film 13 is eliminatedonly from the area above the switching element 1.

[0090] On the upper layer of the foregoing active matrix substrate, aconversion layer 16 made of selenium is vapor-deposited, for example, bythe vacuum deposition. On the conversion layer 16, deposited is a goldlayer 17 to be patterned into an electrode for applying a voltage to theconversion layer 16, thereby forming a substrate of the image sensor. Inthis example, the conversion layer, a positive bias voltage is appliedby a power source 18.

[0091] According to the foregoing active matrix substrate, theinterlayer insulating film 13 is formed between the scanning lines 3,the scanning lines 4, and the pixel electrodes 14, and it is thereforepossible to form the pixel electrodes 14 over the signal lines 4. Withthe forgoing characteristic structure, the aperture ratio can beimproved, and at the same time, operation inferior of the conversionlayer 16 can be suppressed by shielding it from the electric fieldgenerated by the signal lines 4 and the scanning lines 3. By adoptingthe interlayer insulating film 13 of a sufficient thickness and of lowdielectric constant, an increase in capacitance and a reduction in S/Nratio can be suppressed even in the foregoing structure of forming thepixel electrodes 14 over the source signal lines 4.

[0092] In the area above the switching element 1, the transparentdielectric layer 14 b extended from the pixel electrode 14 is formed viathe dielectric layer 22. With this structure, the transparent dielectriclayer 14 a functions as a top gate of the dual-gate transistor, and theswitching element 1 conducts at potential slightly higher than thethreshold potential, thereby releasing excessive electric charge intothe source signal line 4.

[0093] In the foregoing structure, when the electric change is releasedat a potential slightly higher than the threshold potential, the DCvoltage of low level is applied to the switching element 1, and when avoltage of higher level is applied, the switching element 1 stronglyconducts and can release the electric charge at extremely low timeconstant. Namely, as compared to the interlayer insulating film 63 ofseveral μm, the dielectric layer 22 in the thickness of several hundredsof Å where the pixel electrode is closer to the gate insulating film 7for use in the gate electrode 6 and the bottom gate of the dual gate ismore suited for the above condition, and thus offers greater effects ofpreventing the foregoing problem of variations in characteristics amongpixels.

[0094] The dielectric layer 22 is formed by the vapor deposition such asCVD (Chemical Vapor Deposition) method whose thickness can be adjustedin a simpler manner than the film thickness adjustment of the interlayerinsulating film 63 (see FIG. 8) formed by the spin coating method.Moreover, the dielectric layer 22 made of silicon nitride or siliconoxide offers stable properties unlike the organic film. Therefore,changes in characteristics of the insulating film caused by the electricfield in the operation of the optical sensor is less likely to occur.The foregoing advantageous characteristics are very important inpreventing an increase in leak current due to variations in switchingeffects by the top gate being used or deteriorations in high voltageprotection function.

[0095] In the foregoing preferred embodiment, explanations have beengiven through the case wherein positive electric charge is stored in thepixel electrode 14, and when excessive electric charge is stored in thepixel electrode 14, a positive bias voltage is applied to the switchingelement 1 to conduct it, to allow excessive electric charge to bereleased. However, the switching element of the present invention is notlimited to the above, and for example, p-type channel transistor may beadopted. In this case, negative electric charge generated from theconversion layer 16 with an application of negative vias charge isstored in the pixel electrode 14, and when excessive electric charge isstored in the pixel electrode 14, negative bias voltage is applied tothe switching element 1 to conduct it to allow excessive electric chargeto be released. Needless to mention, the foregoing structure using anegative bias voltage offers the same effects as achieved from theforegoing structure of the above preferred embodiment.

[0096] [Second Embodiment]

[0097] The following descriptions will discuss another embodiment of thepresent invention in reference to FIG. 3. For ease of explanation,members (structures) having the same functions as those shown in thedrawings pertaining to the first embodiment above will be given the samereference symbols, and explanation thereof will be omitted here.

[0098]FIG. 3 is a cross sectional view of an image sensor in accordancewith the second embodiment of the present invention. The image sensor ofthe present embodiment basically has the same structure as the imagesensor of the first embodiment illustrated in FIG. 1 and FIG. 2 exceptfor the following structure. In the image sensor of the presentembodiment, in an area above the switching element 1, a transparentdielectric layer 14 a extended from the pixel electrode 14 is formed vianot only a protective film 12 (dielectric layer) but also the interlayerinsulating film 13. Namely, the image sensor of the present embodimentdiffers from the image sensor of the previous embodiment in that, theinterlayer insulating film 13 and the transparent electricallyconductive film 14 a are formed on the protective film 12 in the channelregion of the switching element 1.

[0099] The foregoing structure of the present embodiment offers theeffect as achieved from the structure illustrated in FIG. 9 and theeffect as achieved from the structure illustrated in FIG. 1 and FIG. 2,i.e., an improved reliability of the switching element 1, and preventionof a leak current due to a top gate at low voltage. Moreover, accordingto the structures illustrated in FIG. 1 and FIG. 2, in the area abovethe switching element, which has the roughest surface in the activematrix substrate contacts the conversion layer 16 only via thedielectric layer 22, and with the single use of this dielectric layer22, the roughness may not be absorbed completely. In response, the imagesensor of the present embodiment is structured so as to form theinterlayer insulating film 13 and the transparent dielectric layer 14 aon the protective film 12 (dielectric layer) to make the surfacesmoother. With this structure, even when adopting the conversion layer16 made of selenium which is liable to be crystallized by theprotrusions and recessions of the rough surface, it is still possible toform films under stable conditions.

[0100] The thickness of the interlayer insulating film 13 may beselected such that optimal characteristics can be achieved when used incombination with the protective film 12. Specifically, first, the totalamount of electrostatic capacitance is set such that i) thecurrent-voltage condition in which the switching element 1 can be surelyprevented from being destroyed against high voltage, and ii) thecondition of preventing leak current in normal operations can bewell-balanced, and the film thickness of the protective film 12(inorganic film) and the film thickness of interlayer insulating film 13(organic film) which prevents an inferior in the conversion layer 16 maybe set so as to satisfy the total amount of electrostatic capacitance asset.

[0101] [Third Embodiment]

[0102] The following descriptions will discuss still another embodimentof the present invention in reference to FIGS. 4 and 5. For ease ofexplanation, members (structures) having the same functions as thoseshown in the drawings pertaining to the first and second embodimentsabove will be given the same reference symbols, and explanation thereofwill be omitted here.

[0103]FIG. 4 shows a cross sectional view of an image sensor inaccordance with the third embodiment of the present invention. The imagesensor of the present embodiment differs from the image sensor of thesecond embodiment illustrated in FIG. 3 in the following structure. Thatis, the interlayer insulating film 13 is constituted by an interlayerinsulating film 13 a formed in an area above the switching element 1,and an interlayer insulating film 13 b of the remaining portion. Theinterlayer insulating film 13 is structured such that the interlayerinsulating film 13 a and the interlayer insulating film 13 b havedifferent thicknesses. Specifically, the thickness of the interlayerinsulating film 13 a is set such that the switching element 1 can beprevented from being destroyed against high voltage and in the meantimeleak current in the normal operation can be prevented. On the otherhand, the interlayer insulating film 13 b of the remaining portion isformed thicker than the interlayer insulating film 13 a, i.e., 2 μm sothat a level difference at a portion where the source signal line 4 anda scanning signal line 3 crosses, and a reduction in capacitance betweenthe pixel electrode 14 and the source signal line 4 can be surelysuppressed.

[0104] By adopting the photosensitive organic film for the interlayerinsulating film 13, the foregoing structure can be realized with ease bythe following method. Firstly, the process up to the formation of themetal layer 10 and the transparent electrically conductive film 11 areperformed by the known method of manufacturing a active matrixsubstrate. Then, the dielectric layer (protective film) 12 is formed,and the portion corresponding to the contact hole 15 of the dielectriclayer 12 is removed by etching. Then, photosensitive acrylic transparentresin is applied to the thickness of 2 μm by the spin coating method.Further, after exposing on the switching element 1 with an ultravioletray of low intensity, or with an ultraviolet ray of normal intensity,the portion corresponding to the contact hole 15 is fully exposed. Asthe acrylic transparent resin is positive photosensitive resin, theexposed portion can be removed in the same developing process as that ofthe normal photographic process. On the other hand, the portion abovethe switching element 1 is not fully exposed, and therefore, the upperlayer is not removed be removed completely by developing, and theresidual layer on the switching element 1 is formed in an insulatingthin film 13 a.

[0105] In the foregoing manner, the active matrix substrate of the imagesensor can be formed with ease only by switching exposure withoutincreasing the number of steps in the manufacturing process.Specifically, after forming the interlayer insulating films 13 a and 13b of different thicknesses, the transparent insulating layer for use informing the pixel electrode 14 is formed, and is patterned by etching,thereby forming the active matrix part of the image sensor. With theforgoing method, both a) the portion from which the interlayerinsulating film 13 is removed completely, and b) the portion where thethin film portion 13 a is formed thin have smooth cross sections, as inthe characteristic of the photosensitive organic layer formed bydeveloping in the photographic process, and therefore, the likelihood ofthe foregoing problem can be prevented.

[0106] According to the structure illustrated in FIG. 4, the doublelayer structure of the protective film 12 (dielectric layer) and theinterlayer insulating film 13 are formed between the switching element 1and the pixel electrode 14. However, according to the structure ofadjusting the film thickness of the interlayer insulating film 13 a onthe switching element 1, the discharge characteristic of an excessivevoltage can be controlled by adjusting the film thickness of theinterlayer insulating film 13. It is therefore possible to eliminate thedielectric film 22 provided that the reliability of the switchingelement 1 can be ensured. Without the dielectric layer 22, asillustrated in FIG. 5, the semiconductor layer 8 in the channel regionof the switching element 1 is in direct contact with the interlayerinsulating film 13 a.

[0107] In the case where the organic film contacts the channel portion,due to dispersion of impurities from the interlayer insulating film 13 aof an organic film into the semiconductor layer 8 in the channel region,or a trap level on the interface between the interlayer insulating film13 a and the semiconductor layer 8, it is possible that the abnormalityin characteristics of the switching element 1 occurs, or the reliabililyof the switching element 1 may not be ensured. In that case, thestructure of FIG. 4 should be adopted. On the other hand, in the casethe desirable characteristic and reliability of the switching element 1can be ensured, the structure as illustrated in FIG. 5 without thedielectric layer 22 may be adopted.

[0108] In the foregoing first through third preferred embodiments, theactive matrix substrate, which is a precursor to the sensor in theforegoing example can be manufactured at low costs without requiring anyadditional facilities, because the manufacturing process for liquidcrystal display devices can be used for the manufacturing process ofimage sensors only by adjusting the dimensions of the pixel capacitanceand the time constants of the switching elements to be optimal for imagesensors.

[0109] As described, an image sensor of the present invention forconverting incident electromagnetic wave into electric charge by each ofa plurality of pixel electrodes and sequentially reading the electriccharge from the pixel electrodes via switching elements, so as to outputimage signals, is characterized by including:

[0110] an electrically conductive film formed so as to be extended fromthe pixel electrode to a layer above the switching element; and

[0111] an interlayer insulating film made of an organic film, formed ina layer below each pixel electrode and the electrically conductive film,the interlayer insulating film being structured such that a portionabove the switching element is thinner than the rest of the interlayerinsulating film.

[0112] According to the foregoing structure, an interlayer insulatingfilm is formed between the scanning lines, signal lines, and pixelelectrodes in the active matrix substrate. It is therefore possible toform the pixel electrodes over the signal lines. As a result, animproved aperture ratio can be achieved, and in the meantime, byshielding the conversion layer from the electric field generated by thesignal lines and the scanning lines, an operation inferior of theconversion layer becomes less likely to occur.

[0113] Moreover, the organic film of low dielectric constant can beformed thick with ease, and therefore the electrostatic capacitancebetween the pixel electrode and the source signal line can be suppressedto be small. As a result, an increase in noise due to an increase incapacitance of the source signal lines can be prevented, and an improvedsignal to noise (S/N) ratio can be achieved. Furthermore, the activematrix substrate of the image sensor can be manufactured by themanufacturing process of conventional liquid crystal display devicewithout significant modification, and therefore any additional facilityis not needed.

[0114] Furthermore, the electrically conductive film is extended fromthe pixel electrode over the switching element. Therefore, even if anormal readout operation of a predetermined cycle is not performed dueto a trouble or an error in signal readout program, and unexpectedlylarge electric charge is stored in the pixel electrode, the switchingelement is switched ON at or above a predetermined threshold voltage torelease the excessive electric charge, thereby preventing the switchingelement from being damaged.

[0115] Moreover, by forming the dielectric layer between the switchingelement and the electrically conductive film, such characteristic thatthe thin film transistor is switched ON at or above a predeterminedthreshold voltage is determined by the thickness and the dielectricconstant of the dielectric layer formed between the electricallyconductive film and the switching element, and therefore, the foregoingcharacteristic can be set independently of the interlayer insulatingfilm. Namely, while maintaining optimal excessive voltage dischargecharacteristics, the electrostatic capacitance between the pixelelectrode and the source signal line can be suppressed, and in themeantime, the signal to noise (S/N) ratio can be improved.

[0116] The foregoing image sensor of the present invention may bearranged such that in an area above the switching element, theinterlayer insulating film is formed between the dielectric layer andthe electrically conductive film.

[0117] According to the foregoing structure, in the area above theswitching element, which has the roughest surface in the active matrixsubstrate, formed are not only the dielectric layer but also theinterlayer insulating film made of the organic film. With thisstructure, even such protrusions and recessions of the rough surface,which cannot be absorbed completely by the dielectric layer alone, canbe absorbed to a sufficient level. In this structure, even when adoptinga conversion layer made of selenium, it is still possible to suppresscrystallization due to the protrusions and recessions, and thereforefilms can be formed under stable conditions.

[0118] In the image sensor of the foregoing structure, the interlayerinsulating film is structured such that at least a portion correspondingto the channel region of the switching element is formed thinner thanother portion of the interlayer insulating film.

[0119] In the foregoing structure, the excessive voltage dischargecharacteristic is determined by the thickness and the dielectricconstant of the interlayer insulating film in the portion between theelectrically conductive film extended from the pixel electrode and theswitching element. It is therefore possible to set the foregoingcharacteristic independently of the interlayer insulating film in theportion for use in forming the electrostatic capacitance between thepixel electrode and the source electrode. Namely, with the foregoingstructure, an improved S/N ratio can be achieved while maintainingoptimal excessive voltage discharge characteristic.

[0120] Another image sensor of the present invention for convertingincident electromagnetic wave into electric charge by each of aplurality of pixel electrodes and outputting image signals bysequentially reading out the electric charge from the pixel electrodesvia switching elements is characterized by including:

[0121] an electrically conductive film formed so as to be extended fromthe pixel electrode to a portion above each switching element; and

[0122] an interlayer insulating film made of an organic film, formedbelow each pixel electrode, the interlayer insulating film beingstructured such that a portion above the switching element is thinnerthan other portion of the interlayer insulating film.

[0123] In the foregoing structure, the excessive voltage dischargecharacteristic is determined by the thickness of the dielectric constantof the portion between the electrically conductive film extended fromthe pixel electrode and the switching element, and therefore, it ispossible to set the foregoing characteristic independently of theinterlayer insulating film in the portion for use in forming theelectrostatic capacitance between the pixel electrode and the sourceelectrode. Namely, with the foregoing structure, an improved S/N ratiocan be achieved while maintaining optimal excessive voltage dischargecharacteristic.

[0124] The foregoing image sensor of the present invention may becharacterized in that the interlayer insulating film is made of aphotosensitive organic film.

[0125] According to the foregoing structure, in the area above theswitching element, which has the roughest surface in the active matrixsubstrate, formed are not only the dielectric layer but also theinterlayer insulating film made of the organic film. With thisstructure, even such protrusions and recessions of the rough surface,which cannot be absorbed completely by the dielectric layer alone, canbe absorbed to a sufficient level. In this structure, even when adoptinga conversion layer made of selenium, it is still possible to suppresscrystallization due to the protrusions and recessions, and thereforefilms can be formed under stable conditions.

[0126] The method of manufacturing an image sensor of the presentinvention is characterized by including the steps of:

[0127] forming a plurality of switching elements, a plurality ofscanning lines and a plurality of signal lines on an insulatingsubstrate;

[0128] forming an interlayer insulating film made of a photosensitiveorganic film in respective portions above the plurality of switchingelements, scanning lines and signal lines,

[0129] exposing and developing a resulting photosensitive organic film;

[0130] forming pixel electrodes on the interlayer insulating film; and

[0131] forming conversion means on the pixel electrodes for convertingan incident electromagnetic wave into electric charge,

[0132] wherein exposure with respect to the photosensitive organic filmis varied between at least a portion of an area above each switchingelement and other portion of the photosensitive organic film.

[0133] According to the foregoing structure, the protrusions andrecessions resulting from the patterning of the wires in layer below theinterlayer insulating film can be suppressed by the interlayerinsulating film, and an inferior in characteristics of the conversionmeans for converting an incident X-ray into electric change on the upperlayer can be prevented. Moreover, by adopting photosensitive resin, asmooth cross section can be achieved even at the pattern edge of theinterlayer insulating film, and therefore it is possible to more surelyprevent an inferior characteristic of the conversion means. Furthermore,as the pixel electrodes can be formed over the source electrodes, anarea occupied by the pixel electrodes can be increased, and therefore,it is possible to collect the electric charge generated from theconversion means in an efficient manner. In the foregoing structure,even if a normal readout operation of a predetermined cycle is notperformed due to a trouble or an error in signal readout program, andunexpectedly large electric charge is stored in the pixel electrode, theswitching element is switched ON at or above a predetermined thresholdvoltage to release the excessive electric charge, thereby preventing theswitching element from being damaged. Moreover, while maintainingoptimal excessive voltage discharge characteristics, the electrostaticcapacitance between the pixel electrode and the source signal line canbe suppressed, and in the meantime, the signal to noise (S/N) ratio canbe improved.

[0134] Furthermore, the interlayer insulating film of the portiondetermining the excessive voltage discharge characteristic of theswitching element and the interlayer insulating film of the portiondetermining the electrostatic capacitance between the pixel electrodeand the source signal line can be formed in thickness as desired byadjusting the exposure, thereby controlling respective physical valuesto be optimal values with ease without increasing the manufacturingsteps.

[0135] Such variations are not to be regarded as a departure from thespirit and scope of the invention, and all such modification as would beobvious to one skilled in the art are intended to be included within thescope of the following claims.

What is claimed is:
 1. An image sensor, comprising: a conversion sectionfor converting an incident electromagnetic wave into electric charge;pixel electrodes for storing the electric charge generated by saidconversion section; switching elements for controlling reading out ofthe electric charge from the pixel electrodes; an interlayer insulatingfilm made of an organic film formed under each pixel electrode; anelectrically conductive film which is electrically connected to saidpixel electrodes, and which is extended from the pixel electrode to alayer above each switching element; and a dielectric layer formedbetween the switching element and said electrically conductive film. 2.The image sensor as set forth in claim 1, wherein in an area above eachswitching element, said electrically conductive film contacts saiddielectric layer without having said interlayer insulating film inbetween.
 3. The image sensor as set forth in claim 1, wherein: saidswitching element is a dual-gate transistor, and said electricallyconductive film functions as one of gate electrodes of said dual-gatetransistor.
 4. The image sensor as set forth in claim 3, wherein: eachswitching element including its channel region is covered with saiddielectric layer, said electrically conductive film is extended from thepixel electrode to an area above said switching element including itschannel region, and in an area above each switching element, saidelectrically conductive film contacts said dielectric layer withouthaving said interlayer insulating film in between.
 5. The image sensoras set forth in claim 1, wherein said conversion section is made ofselenium.
 6. The image sensor as set forth in claim 1, wherein: theelectric charge stored in said pixel electrode is a positive charge, andsaid switching element conducts with an application of a positive biasvoltage.
 7. The image sensor as set forth in claim 1, wherein: theelectric charge stored in said pixel electrodes is positive charge, andsaid switching element conducts with an application of a positive biasvoltage.
 8. The image sensor as set forth in claim 1, wherein: in anarea above said switching element, said interlayer insulating film isformed between said dielectric layer and said electrically conductivefilm.
 9. The image sensor as set forth in claim 8, wherein: saidinterlayer insulating film is structured such that at least a portionabove said switching element is formed thinner than other portion ofsaid interlayer insulating film.
 10. The image sensor as set forth inclaim 8, wherein: said interlayer insulating film is structured suchthat at least a portion corresponding to the channel region of theswitching element is formed thinner than other portion of saidinterlayer insulating film.
 11. The image sensor as set forth in claim9, wherein: said interlayer insulating film is made of a photosensitiveorganic film.
 12. An image sensor for converting incidentelectromagnetic wave into electric charge by each of a plurality ofpixel electrodes and outputting image signals by sequentially readingout the electric charge from the pixel electrodes via switchingelements, comprising: an electrically conductive film formed so as to beextended from the pixel electrode to a portion above each switchingelement; and an interlayer insulating film made of an organic film,formed below each pixel electrode and said electrically conductive film,said interlayer insulating film being structured such that a portionabove said switching element is thinner than other portion of saidinterlayer insulating film.
 13. The image sensor as set forth in claim9, wherein: said interlayer insulating film is structured such that atleast a portion corresponding to the channel region of the switchingelement is formed thinner than other portion of said interlayerinsulating film.
 14. The image sensor as set forth in claim 12, wherein:said interlayer insulating film is made of a photosensitive organicfilm.
 15. The image sensor as set forth in claim 12, wherein: thechannel region of said switching element contacts said interlayerinsulating film.
 16. The image sensor as set forth in claim 1, wherein:said dielectric layer is an inorganic film.
 17. The image sensor as setforth in claim 1, wherein: a double layer structure of the dielectricfilm of an inorganic film and the interlayer insulating film of anorganic film is formed under said pixel electrode, in an area above eachswitching element, said electrically conductive film contacts saiddielectric layer without having said interlayer insulating film inbetween.
 18. The image sensor as set forth in claim 1, comprising: asignal line for transferring electric charge as collected in each pixelelectrode via a switching element, wherein said pixel electrode isformed over the signal line having said interlayer insulating film inbetween.
 19. The image sensor as set forth in claim 12, comprising: asignal line for transferring electric charge as collected in each pixelelectrode via a switching element, wherein said pixel electrode isformed over the signal line having said interlayer insulating film inbetween.
 20. A method of manufacturing an image sensor, comprising thesteps of: forming a plurality of switching elements, a plurality ofscanning lines and a plurality of signal lines on an insulatingsubstrate; forming an interlayer insulating film made of aphotosensitive organic film in respective portions above said pluralityof switching elements, scanning lines and signal lines, exposing anddeveloping a resulting photosensitive organic film; forming pixelelectrodes on said interlayer insulating film; and forming conversionmeans on said pixel electrodes for converting an incidentelectromagnetic wave into electric charge, wherein exposure with respectto the photosensitive organic film is varied between at least a portionof an area above each switching element and other portion of thephotosensitive organic film.
 21. The method of manufacturing an imagesensor as set forth in claim 20, wherein: said exposure to saidphotosensitive organic film is adjusted such that a portion above theswitching element of said interlayer insulating film is thinner thanother portion of said interlayer insulating film.